Robert M. Walker, Ph.D., professor of physics in Arts & Sciences and a faculty fellow of the McDonnell Center for the Space Sciences, died Thursday, Feb. 12, 2004, in Brussels, Belgium. He was 75.
Walker worked on the frontiers of space research for more than four decades.
He was the inaugural director of the McDonnell Center, which was established in 1975 by a gift from aerospace pioneer James S. McDonnell. Walker played a key role in planning the return of samples by the Apollo missions and in pathbreaking laboratory studies of moon rocks.
In the past two decades, he was a world leader of microanalytical studies of tiny grains preserved for eons in meteorities, culminating in their identification as stardust.
He was elected to the National Academy of Sciences in 1973.
“Bob was such a dominant force for excellence in our department and the University over so many years, it is hard to grasp that he is gone,” said John W. Clark, Ph.D., chair of physics, the Wayman Crow Professor and a faculty fellow of the McDonnell Center.
“His passion for life and science was an inspiration to us all, and his legacy will endure in the work of his many colleagues and the extended family of his former students.”
Before his death, the Board of Trustees had voted to honor Walker in May with the University’s highest distinction, an honorary doctor of science degree. Walker’s wife, Ghislaine Crozaz, Ph.D., professor of earth and planetary sciences in Arts & Sciences, plans to accept the degree in his honor.
Walker joined the faculty in 1966 as the first McDonnell Professor of Physics and director of a new Laboratory for Space Sciences.
He led the McDonnell Center, which includes one of the world’s largest research groups dedicated to the search for and investigation of extraterrestrial materials, until 1999.
“Washington University would be a lesser institution without the contributions of Bob Walker,” said William H. Danforth, chancellor emeritus and vice chairman of the Board of Trustees.
“He gave us inspiration, enthusiasm, great science and visionary leadership. He built the strength of the McDonnell Center for the Space Sciences. He convinced others of the potential for the modern Department of Earth and Planetary Sciences. He had always the respect and affection of us all.”
Walker earned a doctorate from Yale University for research in experimental particle physics. His work at General Electric in the late 1950s on defects in irradiated copper is still regarded as the definitive work on the topic.
In the early 1960s, Walker’s discovery of fossil nuclear particle tracks in minerals was instrumental to new developments in geo-chronology and cosmic ray physics. In particular, his discovery of tracks from nuclei heavier than iron opened a new frontier of cosmic ray physics.
He subsequently pioneered the use of plastics to detect and count such nuclei in cosmic ray balloon flights.
Walker was a member of the NASA committee that allocated samples of the first returned lunar materials, and his laboratory led the way in deciphering their record of lunar, solar system and galactic evolution. Of special importance was the information they gave on the history of solar radiation and cosmic rays.
More recent achievements include the design of micrometeorite capture cells that were flown aboard NASA’s Long Duration Exposure Facility; verification of the extraterrestrial origin of dust particles collected in the upper atmosphere; and the successful search for interstellar grains in meteorites.
The last two decades of Walker’s career were driven by his remarkable vision and his excitement at the prospect of profound discovery. His recognition of the potential importance of the ion microprobe for making isotopic measurements on microscopic samples, and his acquisition in 1982 of a state-of-the-art instrument for the University, led directly to a series of spectacular results.
Chief among these was the identification and characterization of stellar condensates in meteorites, which opened a window into stellar evolution and the creation of the heavier elements.
Always in pursuit of more powerful ways to analyze small amounts of material, Walker devoted the last years of his life to the implementation of nanoscale secondary-ion mass spectrometry — NanoSIMS — promoting the development, acquisition and application of the most advanced instrument of its kind.
This effort was rewarded with the discovery — which he had forecast years earlier — of presolar silicate grains in interplanetary dust particles.
The Robert M. Walker Symposium at the University in March 2003 honored his contributions and achievements.
Walker and his wife maintained a residence in St. Louis County but had been spending much of their time in Brussels.
In addition to his wife, Walker is survived by his sons, Eric and Mark Walker; mother, Dorothy Potter; and three grandchildren.